1. Field of the Invention
The present invention relates to an ink jet recording head for forming a liquid ink droplet by discharging liquid ink from at least one orifice, and more particularly, it relates to an ink jet recording head wherein ink is discharged toward a direction perpendicular to a substrate having a plurality of discharge energy generating means for discharging the ink, and an ink jet recording apparatus having such a head.
2. Related Background Art
Regarding ink jet recording heads of this kind, for example, an ink jet recording method disclosed in the Japanese Patent Application Laid-Open No. 54-51837 has a feature different from the other ink jet recording methods, in the point that a power for discharging a liquid droplet is obtained by applying thermal energy to liquid.
That is to say, the recording method disclosed in the above Japanese Gazette is characterized in that liquid subjected to thermal energy is heated to generate a bubble which discharges a liquid droplet from an orifice provided at an end of a recording head, and the liquid droplets are adhered to a recording material to form an image corresponding to image information.
A recording head used in this method generally comprises a substrate on which electrical/thermal converters for generating thermal energy are provided and a recording head portion formed from resin layers or metal layers for forming liquid passages and a common liquid chamber communicated with liquid discharge orifices, and connection wirings for supplying electrical energy to the electrical/thermal converters and drive circuits are formed on the substrate as printed circuits. Surfaces of the connection wirings and the electrical/thermal converters are coated by an insulating layer made of SiO.sub.2 and the like and a protection layer made of metallic material such as Ta and the like.
Further, for example, as disclosed in the Japanese Patent Application Laid-Open No. 59-95154, there has been proposed a recording head of a type wherein liquid is discharged in a direction perpendicular to a heat acting plane by attaching an orifice plate to a substrate.
FIG. 8 shows an example of a conventional recording head. In this example, a recording head Ho comprises a substrate 210 such as a silicone wafer, a heater board 201 comprised of a resin layer 220 laminated on the substrate, and an orifice plate 202 provided on the resin layer 220, and the substrate 210 is provided at its central portion with an ink supplying aperture 210a. Electrical/thermal converter elements 211 disposed in two rows and electrodes 213 connected to the corresponding electrical/thermal converter elements 211 via connection wirings 212 are arranged on a surface of the substrate 210. The surfaces of these elements 211-213 are covered by an insulation layer (not shown) which is in turn coated on a metallic protection layer. The protection layer serves to prevent the insulation layer from being damaged due to cavitation. Further, the resin layer 220 is provided with liquid passages 221 open to the respective electrical/thermal converter elements 211, and a common liquid chamber communicated with the aperture 210a of the substrate 210. The orifice plate 202 has orifices 202a communicated with the corresponding liquid passages 221 formed in the resin layer 220.
The orifice plate 202 is integrally formed from metal such as nickel, stainless steel or the like, or suitable resin, and is adhered to the surface of the heater board 210 by adhesive or the like.
In such an ink jet recording head, a high speed operation has been requested. In order to achieve the high speed operation, the ink jet recording head can be elongated. That is to say, by increasing a recording width of the ink jet recording head, the number of dots which can be recorded at a time is increased, thereby improving the recording speed.
As a typical example of such an ink jet recording head, there is an ink jet recording head of full-line type. Since the ink jet recording head of full-line type has a print width (recording width) greater than a width of a recording material (recording medium), the recording can be effected by shifting the recording material without shifting the recording head, thereby achieving high speed recording.
As the above-mentioned ink jet recording head of full-line type wherein ink is discharged in the direction perpendicular to the heat acting plane, there has been proposed an elongated head constituted by adhering an elongated orifice plate 204 to an elongated heater board 203, as shown in FIG. 9.
The orifice plate of the above-mentioned ink jet recording head of full-line type wherein ink is discharged in the direction perpendicular to the heat acting plane generally has a thickness of 20 to 100 .mu.m so that a distance between the orifices and the heat generating portions (heaters) is not so increased. In consideration of such small thickness of the plate and the manufacturing accuracy of the orifices, the orifice plate is normally made of metal or resin. On the other hand, the substrate generally comprises a silicon substrate. When the orifice plate and the substrate are made of different materials in this way, although there is no problem in case of normal size head, if the head is made elongated, due to the difference in coefficient of linear expansion between these materials, during the driving of the heaters or the manufacture of the head, there arises a positional deviation between the heat generating portions and the orifices, which results in the risk that the flying direction of the ink droplet becomes unstable and the orifice plate is peeled from the substrate due to the stress acting in the orifice plate.
When the orifice plate is made of resin, there arises the same problem as mentioned above, because of the curing and contraction of the resin during the curing process.
Further, as mentioned above, since the orifice plate is very thin, it is very difficult to manufacture the elongated orifice plate with high accuracy.